Allow snap-to functionality when moving entities
When creating new entities and moving them into place it would sometimes be of great use to have "snap-to" functionality where the new entity is attached to an already existing entity. This is especially useful when building a wall for example.
Any implementation would probably need to have a certain "sticky radius" defined, which would specify how close the entities needs to be to each other in order for them to snap together.
This functionality should be toggable (we probably don't want it present in the normal entity placement).
* Blueprints in grey have been implemented.